Desiccated filaments restore photosynthetic activity and grow rapidly after rehydration when the rainy season comes. Photosynthetic activity off Microcoleus vaginalus decreased during the process of water loss, and the biomass of mail-made algal crust reached maximum about 27 mu g Ch1 a/cm(2) after inoculated onto unconsolidated sand. It is important for ion concentration in the recovery of photosynthetic activity in rehydration process. Compared with distilled water, photosynthetic activity recovered high after wetted with BG-11 medium. Compared with the recovery of BG-11, photosynthetic activity were inhibited by the deficieney of K+ and Mg2+, and it was retarded by the deficient of Ca2+, while N and A, didn't have a significant change. The recovery of photosynthetic activity was enhanced by the addition of 500mg/L EPS, HWP and 100mg/L sucrose. It indicated that some ion contents (K, P, Mg, Ca2+) played an important role in the recovery of photosynthetic activity, and EPS, HWP and sucrose may play an important role in keeping cell morphology.